Câu 1:
`y=cotx/cosx=cosx/{sinxcosx}`
ĐK: $\sin x\ne 0$, $\cos x\ne 0$
$\Leftrightarrow 2\sin x\cos x\ne 0$
$\Leftrightarrow \sin2x\ne 0$
$\Leftrightarrow x\ne \dfrac{k\pi}{2}$ `(k\inZ)`
Câu 2:
ĐK: $\cos x\ne 0\Leftrightarrow x\ne \dfrac{\pi}{2}+k\pi$
$\sqrt3\tan x=-3$
$\Leftrightarrow \tan x=-\sqrt3$
$\Leftrightarrow x=\dfrac{-\pi}{3}+k\pi$ (TM) `(k\inZ)`